The present invention relates to a system for detecting an angular position of a crankshaft and a specific cylinder of an engine for a motor vehicle, and to a method thereof.
Recently, electronic control systems are used for controlling various components of the engine, such as a fuel injector and a spark plug. The timings of fuel injection and ignition in each cylinder are determined based on crank angle and cylinder number. Accordingly, a crank angle sensor and a cylinder number sensor are provided to detect the crank angle and the cylinder number.
Generally, the sensors are disposed adjacent a disc secured on a camshaft and/or a crankshaft of the engine. Sensing means detect the crank angle and the cylinder number by projections on the periphery of the disc, and generate a crank angle signal and a cylinder discriminating signal in a form of pulse.
In another detecting system, the disc for detecting the crank angle is mounted on the crankshaft and the disc for discriminating the cylinder is mounted on the camshaft. Two discs are necessary in these sensors for detecting the crank angle and the cylinder number, thereby increasing manufacturing cost and complicating the control system.
Japanese Patent Application Laid-Open 1-219341 discloses a detecting system where the crank angle and the cylinder number is determined with a single sensor. The detecting system generates a plurality of reference pulses in one revolution of the disc. The number of the pulses corresponds to the number of the cylinders provided in the engine. A cylinder discriminating pulse is generated after one of the reference pulses is generated. The time intervals between the pulses are measured to obtain a ratio between each interval and the last time interval. The ratio is compared with a predetermined reference value in order to determine whether the latest pulse is the reference pulse or a cylinder discriminating pulse.
However, since the reference pulse is generated once for each cylinder, when the engine speed rapidly increases at acceleration, the ignition timing determined by the reference pulse may be retarded. To a contrary, during the decrease of the engine speed at deceleration, the timing is advanced too much. Thus, the ignition timing is not accurately controlled.
In order to improve the accuracy of the ignition timing control, it has been proposed to provide a detecting system where a plurality of pulses are generated for each cylinder. The intervals between pulses generated at predetermined crank angles of a predetermined cylinder are measured, and the crank angles are determined based on the ratio thereof. However, when the engine speed rapidly changes at acceleration, deceleration and at cranking for starting the engine, the crank angle is erroneously determined. In order to prevent the error, the discrimination of the cylinder number is not completed until several cylinder discriminating pulses are generated, resulting in delaying the decision.